Apparatus for obtaining isotropic irradiation of a specimen

ABSTRACT

Apparatus for moving a film emulsion in a path of high-energy particles so as to obtain essentially an isotropic exposure. The apparatus rotates the film on a turntable along one axis and simultaneously shifts the turntable up and down within a limited range.

United States Patent [72] Inventor Lester Katz Huntsville, Ala.

[2!] Appl. No. 855,004

[22] Filed Sept. 3, 1969 (45] Patented July 13, 19'" I 73] Assignee The United States of America as represented by the Administrator of the National Aeronautics and Space Administration [54] APPARATUS FOR OBTAINING ISOTROPIC IRRADIATION OF A SPECIMEN 5 Claims, 9 Drawing Figs.

52 us. Cl 250/495 a, 250/495 TE, 250/5 l 250/52 51 Int. Cl. .nousms,

HOlj 37/20 [50] Field of Search. 250/495 TE, 49.5 R, 49.5 GC, 49.5 B, I06 R, 52

[56] References Cited UNITED STATES PATENTS 3,240,934 3/1966 Watanabe 250/495 Primary Examiner-James W. Lawrence Assistant Examiner-C. E. Church Attorneys-L. D. Wofford, Jr., C. C. Wells, Jr. and G. T.

McCoy ABSTRACT: Apparatus for moving a film emulsion in a path of high-energy particles so as to obtain essentially an isotropic exposure. The apparatus rotates the film on a turntable along one axis and simultaneously shifts the turntable up and down within a limited range.

PATENTEU JUL I 3 I97! SHEET 2 BF 3 'rT PARALLEL INCIDENT BEAM EMULSION FIG. 3

EMULSION F ONE RAY RESULTING TRACKS INVENTOR LESTER KATZ Q# Q '1 l 1 A C pfi/o' 4 ATTORNEYS ONE INCIDENT RAY F I G. 5

PATENTEDJUL13 I97! 3 Q 593; 024

SHEET 3 0f 3 /O SODEGREE osmou 31 Q) Q Q EMULSON TURNTABLE (8 EMULSION) 5 ATG' O DEGREES TURNTABLE MOTOR FIG.6

, a LENGTH OF ARM nommc FOLLOWER \7[ q RADIUS OF FOLLOWER RADIAL LENGTH CAM WHEN-0* O n (FOLLOWER AT LOWEST Posmom FOLLOWER 37 RADTAL ELEMENT 0-) POSITOON, conncsPouuuc TO FOLLOWER Posmou a FIG.?

IN VE N TOR LESTER KATZ BY 9A2 MW .Q.

ATTORNEYS APPARATUS FOR OBTAINING ISO'I'ROPIC IRRADIATION OF A SPECIMEN ORIGIN OF THE INVENTION The invention was made by an employee of the U.S. Government and may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

l. Field of the Invention The present invention relates to an apparatus for exposing film emulsions and other radiation-sensitive items and more specifically to an apparatus to simulate isotropic radiation, as one might perceive in space, on a film emulsion from a parallel radiation source.

2. Description ofthe Prior Art Films or emulsions are used during spacecraft missions for a variety of scientific purposes. A problem associated with this type of usage arises from the sensitivity of various emulsions to background radiation because storage or use in an environ ment of relatively intense natural radiation may darken some undeveloped films to the extent that objects in the developed film are not sufficiently detectable. Hence, it has become desirable to test film to ensure that its emulsion sensitivity is properly chosen.

Tests by exposure to high-energy particles emanating from an accelerator, however, does not irradiate film in the isotropic mode fuund in space since the particles move in essentially parallel paths. Herebefore, there has been no satisfactory way of exposing the film by placing it in a path of high-energy par ticles and obtaining an isotropic exposure.

SUMMARY OF THE INVENTION In the present invention, an apparatus is provided which provides a turntable to which a film emulsion is adapted to be fixed. The turntable is motor driven so as to rotate about its center axis and face in the general direction of the parallel radiation source. The turntable is also mounted on a cradle which pivots the turntable up and down in an arc according to an action of a special cam simultaneously with the rotation of the turntable whereby the film emulsion could be exposed in essentially an isotropic manner.

Accordingly, it is an object of the present invention to provide an apparatus for exposing flat sheet film to an essentially isotropic distribution of radiation.

Another object is to provide an apparatus of simplicity to accomplish a difficult feat of obtaining isotropic radiation from a parallel ray source.

Other objects and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of the apparatus according to the present invention;

FIG. 2 is a top view of the apparatus of FIG. 1, partly in section for clarity;

FIG. 3 is a two-dimensional view of parallel incident beam and film emulsion;

FIG. 4 is an enlarged view of radiation tracks in a film emulsion from one incident ray;

FIG. 5 is a view illustrating the regions of isotropic operation of the apparatus of FIG. I;

FIG. 6 is a view illustrating schematically the operation of the cam follower and emulsion turntable;

FIG. 7 is a view illustrating the derivation of the cam-follower geometry;

FIG. 8 is a front view of the cam;

FIG. 9 is aside view of the cam.

Referring now to FIG. I wherein is illustrated an apparatus for obtaining isotropic radiation of a film emulsion. The apparatus has a housing defined by a baseplate I I, a middle plate [3 secured to an end of the baseplate and extending vertically therefrom, and two cantilevered arms 15 and I7 extending from the upper end of the middle plate 13 in a direction opposite to the baseplate II. Diagonal braces I9 and 21 extend from the upper side edges of the baseplate I I to the side edges of die middle plate I3 to bring rigidity to the housing.

A channel-shaped cradle 23 composed of a crossmember 25 and two end side members 27 and 29 is rotatively mounted between the two support arms 15 and I7. Each side member 27 or 29 is journaled adjacent its forward end to a contiguous arm 15 or 17, respectively. A cylindrical motor 3] extends through the left support arm 15 at a location near where the cradle 23 is at a maximum distance along the support arms from its journaled shafts. The motor 3! has a shaft which supports a cam 33 having a geometry in the shape of a modified cardioid, the cam 33 being balanced at the shafts center by removing portions 35 of its interior.

The cradle 23 has a roller or wheel 37 journaled onto the crossmember 25 adjacent the left-side arm 15, which rides on the edge surface of the cam 33 so that the cradle 23 will be caused to move up and down. An elongated shaft 39 extends outwardly from the right-side arm, onto which is threaded a counterbalanced weight 4] which balances somewhat the cradle weight about its pivot points but allows the cradle 23 to be the heavier side whereby it will be pulled down against the cam 33.

A cylindrical motor 43 is centrally located on the crossmember 25 of the cradle 23 and the motors shaft extends perpendicular to the longitudinal axis of the crossmember 25. A circular turntable 45 is secured to the end of the motor shaft. The film emulsion which is to be isotropically exposed is secured to the flat face of the turntable. The electrical components 47 for the control of the motors 3] and 43 may be fastened to the upper surface of the baseplate I I.

In operation, the cradle roller 37 starts from the cusp 34 of the modified cardioid-shaped cam 33 (see FIGS. 8 and 9), and as the motor rotates the cam 33, the cradle 23 is first swung upwardly, causing the turntable 45 to swing downwardly, and then the cradle 23 is swung downwardly from its peak until it reaches the cam cusp 34, whereupon, the cradle is swung upwardly again. The cam 33 causes the turntable 45 to expose the emulsion within an included angle of :IS" to as depicted in FIG. 5.

The operation of the apparatus will be more fully understood by referring to FIG. 3 which shows a film emulsion 6| receiving parallel incident radiation while the emulsion 61 is rotated about an axis through point 2, perpendicular to the plane of the drawing. The unit normal (3) is shown at the emulsions polar axis of symmetry. If the angle which the parallel beam makes at any time with His 0, then the intensity of the beam upon the flat emulsion will be N cos 01.4, where N number of protons per second and A area of parallel beam. Since it is desired that the time rate of change of the intensity to be constant so as to imply an isotropic flux, the relationship is expressed using differential calculus as follows:

d(N cos B/A) where C is another constant,

The symbol t represents time measured in seconds. The quantity d0/dt is the relative angular velocity at 0 which the emulsion must have about a perpendicular through point 0 so that the parallel incident beam can be effectively seen as an isotropic distribution. This velocity profile is generated by the special cam and follower mechanism shown in FIG. I as will be explained further hereafter.

An application of the branch of mechanical engineering known as kinematics of machinery shows that the cam 33 will be able to continuously cycle the emulsion at most, from only 6=0 to 90 and return. FIG. 4 illustrates this mode of operation and shows the radiation tracks caused by one ray.

While obviously, the to 90 sweep is not an adequate isotropic distribution, if the emulsion is rotated at a constant velocity about its polar axis (coincident with Ti) as the emulsion is simultaneously rotated about point 0 with the velocity dO/dr, the tracks will have a three-dimensional isotropic distribution, limited to half-space exposures.

The cam 33 of FIG. I provides the dflld! angular velocity to the cradle 23, which rocks the turntable 45 and its attached emulsion. The turntable motor 43 simultaneously spins the emulsion about ii.

The cam profile, a modified cardioid, is developed from the previously derived equation dfi/dt =c/Sin 9. Assuming C l, the following integral equation can be set up, with the subscript o" meaning initial.

Then,for an excursion of 059590 the choice of C=l implies a rotation of the emulsion from 0 to 90 in I second (see FIG. 6). Once the mechanism has been designed on this unit basis it may be operated at any multiple of this speed and with apparatus of FIG. I, a cam rotation of IO r.p.m. and turntable rotation of 350 r.p.m. are the nominal operating speeds. If 11 is the angle which any radial line from the center of rotation of the cam 33 makes with that vertical radial line corresponding to the follower position at 0=0, then d l /dt=K, where K is the angular speed of the cam motor.

FIG. 6 depicts the essential geometry of the cam 33 and follower 37. When the cam 33 has rotated d the follower is at 8. However, the follower 37 does not lie vertically above A, the cam center, but is at a lag angle a from the vertical. This angle is given by with its solution R R cos 0 R sin 0 r; r,, where R length of arm-holding follower r,= radius of follower r radial length of cam when 9 0 (follower at lowest position) The length of the radial cam element corresponding to follower position is a tan- From the former equation fora If the cam 33 were to turn one revolution while the emulsion turntable 45 rotated 90, there would be a discontinuity in the cam,since P y P To circumvent this ditficultyJhe cam 33 is caused to turn one-half revolution for a 90 rotation of the turntable. This leads to a singleaxissymmetry cam 33 which has the profile of a modified cardioid and a cam motor speed of K=l 80/sec. For any given 6 position of the follower 37, the lag angle a must be added to 0 in order to obtain the true cam angle (0+0) corresponding to the cam radial element P which is in contact with the follower at that instant. Because so that Fl cos 0 when l. I. th t) degrees. and r, seconds.

Also. 3-2 K yields II- 1804 l -cos 6), upon integration 2 dt sin 6 the angular acceleration is r2 1 d8 sin 6 At 0=0, the acceleration is infinite. This corresponds to the cusp of a modified cardioid. Since the follower would have to be physically as small as a point to follow the cam profile into the cusp 34 (see FIG. 9), and since the angular acceleration is so large in that region, an engineering trade-off is made which allows the follower 37 to start its motion at 0=l5 instead of 0. Because of the lag angle a, when the cam angle is I", the follower angle is 83. These are the regions of isotropic opera tion shown in FIG. 5.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. it is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What 1 claim is:

1. An apparatus for obtaining isotropic radiation ofa film emulsion, comprising:

a housing having two spaced-apart supports,

a channel-shaped cradle defined by a main crossmember with one side member extending from one end and another side member extending from the other end,

said cradle extending between said two supports with one cradle side member adjacent its distal end journaled to one of the supports and the other cradle side member adjacent its distal end journaled to the other of said sup- P a cam having an edge surface substantially in the shape of a cardioid,

power means secured to one of said supports and rotatively supporting said cam between said side members,

said cam having its edge surface acting against said main Crossmember of said cradle so as to cause the cradle to pivot up and down along an are slightly less than 180" when said cam is rotated by said power means,

a circular turntable having a center axis parallel to said side members, and a flat face surface extending perpendicular to said side members,

said flat face of said turntable adapted to support a film emulsion toward a parallel radiation source, and

a motor means attached to said main crossmember and sup porting said turntable for rotation about its center axis.

2. An apparatus as defined by claim 1 wherein said cradle has counterbalance means extending from one cradle side member forwardly of the journal for that side member and housing support.

3. An apparatus as defined by claim I wherein said power means rotates said earn at a nominal speed at l0 r.p.m. and said motor means rotates said turntable at a nominal speed at 350 r.p.m.

4. An apparatus as defined by claim 1 wherein said cam pivots said cradle and its turntable along an are slightly less than for a cam rotation of about one-half revolution.

5. An apparatus as defined by claim 3 wherein said cam pivots said cradle and its turntable along an arc of about 90 for a cam rotation of about one-half revolution. 

2. An apparatus as defined by claim 1 wherein said cradle has counterbalance means extending from one cradle side member forwardly of the journal for that side member and housing support.
 3. An apparatus as defined by claim 1 wherein said power means rotates said cam at a nominal speed at 10 r.p.m. and said motor means rotates said turntable at a nominal speed at 350 r.p.m.
 4. An apparatus as defined by claim 1 wherein said cam pivots said cradle and its turntable along an arc slightly less than 90* for a cam rotation of about one-half revolution.
 5. An apparatus as defined by claim 3 wherein said cam pivots said cradle and its turntable along an arc of about 90* for a cam rotation of about one-half revolution. 